We identified MIG6 (gene symbol ERRFI1) as a phosphorylation target of mutant EGFRs in our mass spectrometry-based experiments. MIG6, also known as ERBB receptor feedback inhibitor 1 (ERRFI1) and receptor-associated late transducer (RALT), is a scaffolding adaptor protein whose expression is rapidly induced by a variety of growth factors (including EGF) and by hormones and other stressors. MIG6 negatively regulates EGFR, ERBB2, and several other receptor tyrosine kinases and their signaling pathways. We hypothesized that loss of MIG6 may cooperate with mutant EGFR to induce lung tumorigenesis. To test this hypothesis we crossed doxycycline inducible mutant EGFR transgenic mice with Mig6 null mice. Upon doxycycline induction of mutant EGFRs that are expressed in type II epithelial cells, lung tumorigenesis is indeed accelerated upon loss of Mig6 expression. We have completed the survival curve upon doxycycline induction of mutant EGFRs in wild type, heterozygous and knock-out mice. We convincingly show that tumorigenesis is accelerated in Mig6 null background suggesting that Mig6 is indeed a tumor suppressor in mutant EGFR-induced lung tumorigenesis. We have completed the evaluation of histology of mouse lung tumor in various genotypes in collaboration with Dr. Ilona Linnoila. We have also initiated a collaboration with Dr. Mark Simpson to quantify immunohistochemical staining of various targets in these tumors. We have performed biochemical experiments to elucidate the functional role of increased tyrosine phosphorylation at Y394 and Y395 of ERRFI1. We have demonstrated that there is increased interaction of mutant EGFRs and Mig6. In addition Y394/395 are the predominant sites of phosphorylation in Mig6. There is constitutive phosphorylation of these sites in lung adenocarcinoma cells harboring mutant EGFRs. Phosphorylation is significantly inhibited by erlotinib treatment of lung adenocarcinoma cells that harbor TKI-sensitizing mutants of EGFR, suggesting MIG6 is indeed a target of mutant EGFR signaling. We have also demonstrated that MIG6 cannot promote mutant EGFR degradation contrary to its effects on WT EGFR. This is likely due to hyperphosphorylation of Y394/395 of MIG6. These findings have been published (Cancer Discov. 5(5):534-49 (2015). We have continued our studies to understand the biology of Mig6 inhibition in mutant EGFR-driven lung tumor maintenance. We are currently breeding mice to have mutant EGFR, CCSP-rtTA, and Nkx2.1-CreERT2 transgenes in the background of floxed Mig6. We will first generate lung adenocarcinomas in these mice by doxycycline induction. The mouse tumors will be followed by serial MRI imaging. Mig6 will be deleted by tomoxifen injection after the mouse tumors have developed and the subsequent progression of tumor growth will be monitored by serial MRI scan. The overall goal of this part of the project is to examine the role of Mig6 in mutant EGFR-driven tumor maintenance.